02 F150 SCrew 5.4L V8 Plug Problems

A couple of years ago, I had the plugs changed out around 90,000Km. Probably early, but I didn't know any better and thought I would do it as preventative maintenance. I paid someone to do it since it the p[lugs are so hard to get at. Well about 1.5 year after a plug blew out on the passenger side 3rd in from the front. Took it to someone else and he installed a heli-coil and a new plug, rest was OK, but it still cost $500. Ten I asked him to check the rest and torque them all which he unbelievably charged me another $200 for. I stopped going to him after that. Now around a year later another plug blew, or at least I thought so. This time it is passenger side 1st from the front. I haven't done anything yet, but I did look down the hole with a flashlight and noticed the plug is still in the hole! I took a magnet and tried to see if the plug was loose, but it wasn't. I started looking around and found the coil is destroyed, a vacuum line is melted and found a rather larger (about 1" diameter) hole in the side of the manifold right beside where the coil was blown off the plug. Now what I am wondering is did the coil just let go and then it arced and blew the hole in the manifold or is the plug the cultprit or did the manifold explode somehow and take out the coil? I think I can replace all the parts myself and save a bunch of labour charges, but I would like to figure out what the heck happened so that I do not replace them and then have it happen again right away! Any help would be much appreciated.

Turns out the plug had melted and blew out a hole on either side of it. The head is damaged, but the plug did come out. The coile was destroyed and the hole in the manifold was only cosmetic since it was just a spot where the coil had a support, I think. Any way, not vacuum leak. I towed the truck to an engine shop to see how bad it will be. What a POS truck! 99,793km and it is FUBAR.

http://www.autopart.com/tools/toolsmain/tool/T_98140.htm This is a tool for this type of repair.